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Publication numberUS4019920 A
Publication typeGrant
Application numberUS 05/580,136
Publication dateApr 26, 1977
Filing dateMay 23, 1975
Priority dateOct 15, 1974
Publication number05580136, 580136, US 4019920 A, US 4019920A, US-A-4019920, US4019920 A, US4019920A
InventorsEdward A. Burkard, Donald A. Kossuth
Original AssigneeNational Gypsum Company
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Gypsum set accelerator
US 4019920 A
Abstract
A gypsum set accelerator, produced by compression milling a mixture of ground gypsum rock and starch, and the addition thereof to an aqueous slurry of settable calcined gypsum such as in the forming of paper-covered gypsum wallboard.
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Claims(2)
We claim:
1. The method of making gypsum wallboard comprising the steps of compression milling a mixture of from about 1:3 to about 3:1 parts by weight of calcium sulfate dihydrate and starch for a period of time sufficient to reduce the particle size to provide a surface area of about 10,000 to about 20,000 cm2 /gm as measured by a Fisher Sub-Sieve Sizer, mixing said milled mixture into an aqueous slurry comprising the wallboard forming ingredients including a major portion of calcined gypsum and a minor portion water of hydration, fiber reinforcement and density reducing agent, said slurry also including excess water whereby the slurry can be suitably formed, said milled mixture being only separate additive for accelerating the setting and for providing the necessary additional bonding strength needed by the settable gypsum to bond itself to paper cover sheets, disposing said slurry onto paper cover sheets, forming said wallboards of said slurry and paper cover sheets, maintaining said wallboard form while said slurry sets and hardens, and drying said wallboard.
2. The method of claim 1 wherein about 5 lbs. of said milled mixture of about 25 to 75% land plaster and about 25 to 75% starch is added to said aqueous slurry per 1650 lbs. of wallboard core produced.
Description

This application is a division of our copending application, Ser. No. 514,455, filed Oct. 15, 1974, now U.S. Pat. No. 3,920,465, which said application is a continuation of application Ser. No. 358,191, filed May 7, 1973, now U.S. Pat. No. 3,870,538, issued Mar. 11, 1975.

This invention relates to a novel gypsum-starch composition for addition to a calcined gypsum slurry to accelerate the setting of the gypsum, and is particularly directed to an improved method of making gypsum wallboard.

Calcined gypsum, mixed with a proper amount of water, will normally set in about 25 minutes to a hardness such that a one-fourth lb. Gilmore needle will no longer make any substantial indentation, referred to as initial set, and in about 35 minutes to a hardness such that a 1 lb. Gilmore needle will no longer make any substantial indentation, referred to as final set.

Two of the most common uses of calcined gypsum are (1) in forming the core of the well-known paper-covered gypsum wallboards and (2) in forming the relatively thick wall surfacing material in a plastered wall. In making gypsum wallboard it has been common practice to add a set accelerating agent in an amount sufficient to permit the wallboard core to reach initial set in about 3 to 4 minutes, and to reach final set in about 5 to 8 minutes. In preparing bags of calcined gypsum for job site mixture with water for plastering walls it has been common to add set retarders and set stabilizers, which include accelerators, such that when admixed with water and aggregate the final set of the plaster mixture is reached in about an hour to 2 hours.

The gypsum setting reaction involves the reaction of calcium sulfate hemi-hydrate and water to form calcium sulfate dihydrate. A most common form of accelerator for this reaction is calcium sulfate dihydrate. There are many forms of calcium sulfate dihydrate which can be used and many combinations of ingredients with which it is. combined, when used as a set accelerator, depending on which of several alternative characteristics are most important for a particular use.

In preparing bags of plaster for use on job sites for plastering walls, the calcined gypsum, which is the primary ingredient, is commonly fed to the bagging machine while it is still very warm from the calcining process. If a calcium sulfate dihydrate is added at this time, also, it is subject to being partially calcined, that is partially dehydrated, by the heat from the calcined gypsum, thus losing much of its accelerating ability. To prevent this calcining of the accelerator, it has been taught in U.S. Pat. No. 2,078,199 that a general group of water-soluble carbohydrates known as sugar or a material intermediate between starch and sugar, such as soluble dextrin, can be ball-milled together with the calcium sulfate dihydrate in a weight ratio of 5-25:100 and this water-soluble carbohydrate will function as a dehydration-preventing substance when the combination is used as an accelerator.

The present invention is directed to an improved accelerator for the set of gypsum wherein the primary novel characteristics have no relation to the dehydration prevention characteristics described above. The novel accelerator provides completely unexpected and marked advantages when used in the aqueous slurry of calcined gypsum for forming the core of paper-covered gypsum wallboard.

A common accelerator presently used in the manufacture of gypsum wallboard is fresh finely ground gypsum block. This finely ground block combined with calcined gypsum at a weight ratio of about 0.525:100 will provide setting times suitable for wallboard manufacture, however it must be used substantially immediately after grinding, and, secondly, once the wallboard core has set, this ground block in effect dilutes the strength providing elements of the core, or to state it another way, it reduces the effective core purity.

The accelerator of the present invention consists essentially of the compression-milled product of a mixture of calcium sulfate dihydrate and starch. In a preferred form, the novel accelerator retains its potency for many days and involves the usage of only about 0.175:100 parts of calcium sulfate dihydrate to calcined gypsum. There would also be involved the usage of 0.175:100 parts of starch to calcined gypsum. This starch, however, makes it possible to omit the separate addition of starch to the wallboard core formulation, which is an essential part of prior formulations, and functions through migration to the core to paper interface, to bond the paper to the core in the finished product. Furthermore, the total amount of starch required for providing bond of paper to core is less in accordance with the invention than with prior formulations.

It is an object of the invention to provide a novel accelerator for the setting reaction of calcined gypsum and water.

It is a further object of the invention to provide a novel method of making a gypsum accelerator and of making gypsum wallboard therewith.

It is a still further object of the invention to provide a novel wallboard formulation of substantially lower cost and improved quality.

These and other objects of the invention will be more readily apparent when considered in relation to the preferred embodiments as set forth in the specification and shown in the drawings in which there is a flow chart depicting the process of the present invention.

In accordance with the invention, CaSO4.2H2 O, preferably in the form of crushed natural gypsum rock, is mixed with starch, preferably an inexpensive corn starch, and the mixture is subjected to the action of a ball mill for a time sufficient to cause what appears to be a mechanical combining of the two materials and sufficient to produce a final particle size of about 10,000 to 20,000 cm2 /gm or more particularly from about 12,000 to 18,000 cm2 /gm, and preferably about 15,000 cm2 /gm, as measured by a Fisher Sub-Sieve Sizer.

As shown in the drawing this ball-milled mixture is then mixed with the other ingredients of a gypsum wallboard core, including calcined gypsum, paper pulp, foaming agent and water, and the core is formed between facing papers. Of particular significance, it will be noted that the ball-milled mixture provides both the set accelerator and the core to paper binder in the formulation.

Calcium sulfate dihydrate has been known to be an accelerator, in its original form as mined and finely ground, known as land plaster, and also after it has been calcined and then rehydrated as in block form. The more expensive rehydrated block has been preferred due to its uniform shape and thus its ability to be uniformly ground into a fine accelerator additive. Grinding gypsum rock with abrasive wheels does not produce a uniform rate of feed and it is essential that the plan ground land plaster be used immediately after being ground to a fine powder.

In the present invention, land plaster can be ground to a fineness of about 93% through a 100 mesh screen and stored any convenient time period, and then be uniformly fed to a continuous feed ball mill along with a continuous feed of starch which is obtained at a fineness of about 86% through a 100 mesh screen. Alternatively, the mixture can be ball milled in batches. The mixture, in accordance with the invention, can consist of from about 1 to 99% calcium sulfate dihydrate and from about 99 to 1% starch, however the most unexpected benefits of the invention are obtained with mixtures of about 25 to 75% land plaster and about 75 to 25% starch and particularly a ratio of about 1:1. One of the primary advantages gained by the novel accelerator lies in the unexpected economics provided, and the best economy is obtained by the use of land plaster and raw corn starch as the raw materials.

Some examples of starch suitable with the invention are CPC International (Corn Industrial Division) acid modified corn starch, Lauhoff Grain Company Hi Bond corn starch, A. E. Staley corn starch, Krause Milling Company grain starch, and Grain Processing Corporation pearl starch. The forms of starch which will provide the benefits of the invention include those starches which, when dispersed within a wet, set gypsum core, will migrate to the core to paper interface during drying and provide a bond of paper to core.

In addition to the above method using a ball mill, a rod mill can be used, or any other apparatus wherein the mixed ingredients are subjected to a repeated compression milling treatment.

Following is an example of a prior standard gypsum wallboard core formulation and an example of a preferred embodiment of the present invention, in amounts suitable for making about 1000 sq. ft. of 1/2 inch thick paper-covered gypsum board.

______________________________________                     PRESENT            PRIOR    INVENTION______________________________________Calcined Gypsum    1491    lbs.   1491  lbs.Starch (added separately)              3.4     lbs.   0Paper Pulp Fiber Reinforcement              11.9    lbs.   11.9  lbs.Ground Gypsum Block Accelerator              7.8     lbs.   0Novel Accelerator (1:1 ratio)              0              5.2   lbs.Water of Hydration 140.6   lbs.   140.6 lbs.Soap (foaming agent)              .3      lbs.   .3    lbs.   Core Total      1655    lbs.   1649  lbs.   Front and Back Paper              144     lbs.   144   lbs.   Board Weight    1799    lbs.   1793  lbs.______________________________________

The above two formulas are given as examples both of which will produce good quality 1/2 inch wallboard of about 1800 lbs/M sq. ft. The 6 lbs. difference in weight is of no importance. These two comparative formulas, of slightly different total weight were used to best show the dramatic differences in certain of the individual ingredients in two otherwise similar formulas. All ingredients were kept constant except the starch and accelerator to demonstrate how the novel accelerator, made from 2.6 lbs. of acid modified corn starch and 2.6 lbs. of land plaster, can perform as well as 3.4 lbs. of acid modified corn starch and 7.8 lbs. of ground block added separately.

The "Prior" formula had an initial setting time of 3'35" and a final setting time of 7'35". The "Invention" formula had an initial setting time of 3'25" and a final setting time of 7'10". The bond of paper to the gypsum core was satisfactory in both examples.

In another example of the invention, 5.2 lbs. of a novel accelerator was used having 5% acid modified corn starch and 95% land plaster in place of the 5.2 lbs. of 1:1 ratio novel accelerator above. The setting times were satisfactory but a poor bond of paper to core was obtained. This is corrected for by adding additional starch as a separate ingredient. Thus the novel accelerator of this 5:95 ratio is a satisfactory accelerator in an unexpectedly lower total content but it lacks certain of the other unexpected advantages of the higher starch content accelerator.

In another example of the invention, 5.2 lbs. of a novel accelerator was used made from 50% pearl starch and 50% land plaster, in the above-listed formulation. Pearl starch is an unmodified raw starch. This formulation provided an initial setting time of 2'30" and a final setting time of 4'45", indicating that 5.2 lbs. of this novel accelerator is more than is needed.

In the above formulas, the amount of water of hydration is set forth. An additional amount of water, on the order of 1000 lbs., which is used in making the slurry from which the core is formed, which additional amount is subsequently removed during drying of the wallboard, is not set forth in the formula. It should be realized, however, that with the less solids in the Invention formula than the "Prior" formula, proportionately less additional water, to be subsequently dried off, is required.

The starch content of 3.4 lbs. in the Prior formulation should be recognized as a relatively low example of prior formulations, the range being generally from about 3 lbs. to about 12 lbs., depending on many other factors in the formulation and process, and thus it will be further realized that the 2.6 lbs. of starch which provides a suitable bond in the Invention formula is a marked advantage.

Having completed a detailed disclosure of the preferred embodiments of our invention, so that others may practice the same we contemplate that variations may be made without departing from the essence of the invention.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2853394 *Mar 30, 1953Sep 23, 1958United States Gypsum CoCementitious composition
US2965528 *Nov 9, 1955Dec 20, 1960Celotex CorpGypsum board
US3376147 *Aug 20, 1964Apr 2, 1968Nat Gypsum CoFire resistant wallboard
US3414467 *Sep 3, 1964Dec 3, 1968Keep Chemical CompanyGypsum wallboard and process of making the same
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4132565 *Oct 31, 1977Jan 2, 1979Kaiser Cement & Gypsum CorporationAccelerator for gypsum slurry
US4298394 *Jun 28, 1979Nov 3, 1981Bpb Industries LimitedOrganic gypsum set accelerators
US5277856 *Feb 26, 1992Jan 11, 1994Bison-Werke Bahre & Greten Gmbh & Co. KgMethod for manufacturing shaped bodies from gypsum, water, fibers and light aggregate particles
US6221151Aug 16, 1999Apr 24, 2001National Gypsum CompanyFor accelerating setting reaction of an aqueous calcined gypsum slurry; wallboards
US6585820Nov 16, 2001Jul 1, 2003Fleet Capital CorporationWaxes, complexed starch, alkylphenol and lignosulfate salt or trisodium phosphate; economical; storage stable; room temper-ature pourable; no bactericide required; no separation or curdling on addition to hot or boiling water
US6663707Feb 4, 2003Dec 16, 2003Borden Chemical, Inc.Waterproof slurries of calcium sulfate dihydrate and emulsions comprising waxes, phenols, group I hydroxides, water and starches having storage stability
US6783587Sep 11, 2002Aug 31, 2004National Gypsum Properties, LlcLightweight wallboard compositions containing natural polymers
US7294189Sep 2, 2005Nov 13, 2007Hexion Specialty Chemicals, Inc.Wax emulsion preservative compositions and method of manufacture
US7374610 *Apr 25, 2006May 20, 2008Hexion Specialty Chemicals, Inc.Wax emulsions for gypsum products
US7473712Jun 5, 2003Jan 6, 2009Hexion Specialty Chemicals, Inc.Wax; C24-C34 polymerized methylene-coupled alkylphenol; alkali metal polynaphthalenesulfonate; water; and a starch complexed with e.g., a borate or a molybdenum compound; lignocellulosic composite fiber or particle board that is dimensionally stable when exposed to moisture
US7473713Jun 5, 2003Jan 6, 2009Hexion Specialty Chemicals, Inc.Additives for water-resistant gypsum products
US7488383Jun 3, 2004Feb 10, 2009Hexion Specialty Chemicals, Inc.Gypsum products and method for their manufacture
US7696253Jun 5, 2003Apr 13, 2010Hexion Specialty Chemicals, Inc.Water-resistant additives for gypsum wood fiber products
US8062478Feb 24, 2010Nov 22, 2011Momentive Specialty Chemicals Inc.Gypsum wood fiber articles and methods of making same
US8197952Jun 7, 2010Jun 12, 2012United States Gypsum CompanyHigh starch light weight gypsum wallboard
US8257489Feb 19, 2010Sep 4, 2012United States Gypsum CompanySlurries and methods of making light weight gypsum board
US8262820 *Apr 28, 2006Sep 11, 2012United States Gypsum CompanyMethod of water dispersing pregelatinized starch in making gypsum products
US8303159Sep 5, 2008Nov 6, 2012United States Gypsum CompanyEfficient wet starch preparation system for gypsum board production
US8470461Jun 11, 2012Jun 25, 2013United States Gypsum CompanyLight weight gypsum board
US20110195241 *Feb 25, 2011Aug 11, 2011United States Gypsum CompanyLow Weight and Density Fire-Resistant Gypsum Panel
USRE44070Jun 15, 2012Mar 12, 2013United States Gypsum CompanyComposite light weight gypsum wallboard
DE2930164A1 *Jul 25, 1979Feb 7, 1980Bpb Industries LtdAbbindebeschleuniger fuer gips
DE2930164C2 *Jul 25, 1979Oct 11, 1990Bpb Industries Ltd., London, GbTitle not available
WO2001012569A1 *Jul 13, 2000Feb 22, 2001Nat Gypsum Properties LlcGypsum set accelerator and method of making the same
WO2002033191A1Oct 16, 2001Apr 25, 2002Nat Gypsum Properties LlcCementitious panel with basalt fiber reinforced major surface(s)
Classifications
U.S. Classification106/780, 156/39, 106/665
International ClassificationC04B28/14
Cooperative ClassificationC04B28/14
European ClassificationC04B28/14
Legal Events
DateCodeEventDescription
Oct 3, 1994ASAssignment
Owner name: NATIONAL GYPSUM COMPANY
Free format text: ASSIGNMENT AND RELEASE, SATISFACTION AND DISCHARGE OF MORTGAGE OF PATENTS AND PATENT LICENSES;ASSIGNOR:GENERAL ELECTRIC CAPITAL CORPORATION;REEL/FRAME:007153/0387
Effective date: 19940912
Sep 13, 1993ASAssignment
Owner name: GENERAL ELECTRIC CAPITAL CORPORATION, CALIFORNIA
Free format text: LICENSE;ASSIGNOR:NATIONAL GYPSUM COMPANY A CORP. OF DELAWARE;REEL/FRAME:006723/0785
Effective date: 19930630
Owner name: NATIONAL GYPSUM COMPANY, NORTH CAROLINA
Free format text: PARTY RELEASING LIENS;;ASSIGNOR:GENERAL ELECTRIC CAPITAL CORPORATION, A NEW YORK CORPORATION;REEL/FRAME:006768/0726
Effective date: 19930709
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:NATIONAL GYPSUM COMPANY, A DELAWARE CORPORATION, NOW NAMED ABESTOS CLAIMS MANAGEMENT CORPORATION;REEL/FRAME:006768/0694
Effective date: 19930701
Dec 19, 1990ASAssignment
Owner name: GENERAL ELECTRIC CAPITAL CORPORATION, A CORP. OF N
Free format text: SECURITY INTEREST;ASSIGNOR:NATIONAL GYPSUM COMPANY;REEL/FRAME:005548/0167
Effective date: 19901029
May 18, 1987ASAssignment
Owner name: AMERICAN OLEAN TILE COMPANY, INC., PENNSYLVANIA
Free format text: RELEASED BY SECURED PARTY;ASSIGNOR:CITICORP INDUSTRIAL CREDIT, INC.;REEL/FRAME:005770/0224
Effective date: 19870421